/*
 * Copyright 2002-2016 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.context.config;

import org.w3c.dom.Element;

import org.springframework.beans.factory.config.PropertyPlaceholderConfigurer;
import org.springframework.beans.factory.support.BeanDefinitionBuilder;
import org.springframework.beans.factory.xml.ParserContext;
import org.springframework.context.support.PropertySourcesPlaceholderConfigurer;
import org.springframework.util.StringUtils;

/**
 * Parser for the {@code <context:property-placeholder/>} element.
 *
 * @author Juergen Hoeller
 * @author Dave Syer
 * @author Chris Beams
 * @since 2.5
 */
class PropertyPlaceholderBeanDefinitionParser extends AbstractPropertyLoadingBeanDefinitionParser {

    private static final String SYSTEM_PROPERTIES_MODE_ATTRIBUTE = "system-properties-mode";

    private static final String SYSTEM_PROPERTIES_MODE_DEFAULT = "ENVIRONMENT";


    @Override
    protected Class<?> getBeanClass(Element element) {
        // As of Spring 3.1, the default value of system-properties-mode has changed from
        // 'FALLBACK' to 'ENVIRONMENT'. This latter value indicates that resolution of
        // placeholders against system properties is a function of the Environment and
        // its current set of PropertySources.
        if (SYSTEM_PROPERTIES_MODE_DEFAULT.equals(element.getAttribute(SYSTEM_PROPERTIES_MODE_ATTRIBUTE))) {
            return PropertySourcesPlaceholderConfigurer.class;
        }

        // The user has explicitly specified a value for system-properties-mode: revert to
        // PropertyPlaceholderConfigurer to ensure backward compatibility with 3.0 and earlier.
        return PropertyPlaceholderConfigurer.class;
    }

    @Override
    protected void doParse(Element element, ParserContext parserContext, BeanDefinitionBuilder builder) {
        // 解析并且设置基本属性
        super.doParse(element, parserContext, builder);

        builder.addPropertyValue("ignoreUnresolvablePlaceholders",
                Boolean.valueOf(element.getAttribute("ignore-unresolvable")));

        String systemPropertiesModeName = element.getAttribute(SYSTEM_PROPERTIES_MODE_ATTRIBUTE);
        if (StringUtils.hasLength(systemPropertiesModeName) &&
                !systemPropertiesModeName.equals(SYSTEM_PROPERTIES_MODE_DEFAULT)) {
            builder.addPropertyValue("systemPropertiesModeName", "SYSTEM_PROPERTIES_MODE_" + systemPropertiesModeName);
        }

        if (element.hasAttribute("value-separator")) {
            builder.addPropertyValue("valueSeparator", element.getAttribute("value-separator"));
        }
        if (element.hasAttribute("trim-values")) {
            builder.addPropertyValue("trimValues", element.getAttribute("trim-values"));
        }
        if (element.hasAttribute("null-value")) {
            builder.addPropertyValue("nullValue", element.getAttribute("null-value"));
        }
    }

}
